Screen size/viewing distance is a personal preference. Others can tell you what works best for them which may not necessarily be best for you. The best advice for someone who is unsure of their own preference is to buy the projector first and experiment on a blank wall with different image sizes from your desired viewing distance. You want a projected image to be big enough to be immersive and cinematic when compared with a typical TV but not so big that it causes eyestrain from trying to follow fast moving action. We're all wired a little differently so one size definitely doesn't fit all. That's the reason why some people prefer sitting in the front rows of a commercial cinema, some in the back rows and some in every row in between.